There has been a continuing need for improved bone graft materials. Known autograft materials have acceptable physical and biological properties and exhibit the appropriate structure for bone growth. However, the use of autogenous bone requires the patient to undergo multiple or extended surgeries, consequently increasing the time the patient is under anesthesia, and leading to considerable pain, increased risk of infection and other complications, and morbidity at the donor site.
Alternatively, allograft devices may be used for bone grafts. Allograft devices are processed from donor bone. Allograft devices may have appropriate structure with the added benefit of decreased risk and pain to the patient, but likewise incur the increased risk arising from the potential for disease transmission and rejection. Autograft and allograft devices are further restricted in terms of variations on shape and size.
Unfortunately, the quality of autograft and allograft devices is inherently variable, because such devices are made from harvested natural materials. Likewise, autograft supplies are also limited by how much bone may be safely extracted from the patient, and this amount may be severely limited in the case of the seriously ill or weak.
A large variety of synthetic bone graft materials are currently available for use. Recently, new materials, such as bioactive glass (“BAG”) particulate based materials, have become an increasingly viable alternative or supplement to natural bone-derived graft materials. These new (non-bone derived) materials have the advantage of avoiding painful and inherently risky harvesting procedures on patients. Also, the use of non-bone derived materials can reduce the risk of disease transmission. Like autograft and allograft materials, these new artificial materials can serve as osteoconductive scaffolds that promote bone regrowth. Preferably, the graft material is resorbable and is eventually replaced with new bone tissue.
Many artificial bone grafts available today comprise materials that have properties similar to natural bone, such as compositions containing calcium phosphates. Exemplary calcium phosphate compositions contain type-B carbonated hydroxyapatite [Ca5(PO4)3x(CO3)x(OH)]. Calcium phosphate ceramics have been fabricated and implanted in mammals in various forms including, but not limited to, shaped bodies and cements. Different stoichiometric compositions, such as hydroxyapatite (HA), tricalcium phosphate (TCP), tetracalcium phosphate (TTCP), and other calcium phosphate (CaP) salts and minerals have all been employed in attempts to match the adaptability, biocompatibility, structure, and strength of natural bone. Although calcium phosphate based materials are widely accepted, they lack the ease of handling, flexibility and capacity to serve as a liquid carrier/storage media necessary to be used in a wide array of clinical applications. Calcium phosphate materials are inherently rigid, and to facilitate handling are generally provided as part of an admixture with a carrier material; such admixtures typically have an active calcium phosphate ingredient to carrier ratio of about 50:50, and may have as low as 10:90.
The roles of porosity, pore size and pore size distribution in promoting revascularization, healing, and remodeling of bone have been recognized as important contributing factors for successful bone grafting materials. However, currently available bone graft materials still lack the requisite chemical and physical properties necessary for an ideal graft material. For instance, currently available graft materials tend to resorb too quickly, while some take too long to resorb due to the material's chemical composition and structure. For example, certain materials made from hydroxyapatite tend to take too long to resorb, while materials made from calcium sulphate or B-TCP tend to resorb too quickly. Further, if the porosity of the material is too high (e.g., around 90%), there may not be enough base material left after resorption has taken place to support osteoconduction. Conversely, if the porosity of the material is too low (e.g., 30%) then too much material must be resorbed, leading to longer resorption rates. In addition, the excess material means there may not be enough room left in the residual graft material for cell infiltration. Other times, the graft materials may be too soft, such that any kind of physical pressure exerted on them during clinical usage causes them to lose the fluids retained by them.
Thus, there remains a need for improved bone graft materials that provide the necessary biomaterial, structure and clinical handling necessary for optimal bone grafting. What is also needed are dynamic bone graft materials that provide an improved mechanism of action for bone grafting, by allowing the new tissue formation to be achieved through a physiologic process rather than merely from templating. There likewise remains a need for an artificial bone graft material that can be manufactured as required to possess varying levels of porosity, such as nano, micro, meso, and macro porosity. Further, a need remains for a bone graft material that can be selectively composed and structured to have differential or staged resorption capacity, while providing material than can be easily molded or shaped into clinically relevant shapes as needed for different surgical and anatomical applications. In particular, it would be highly desirable to provide a bone graft material that includes the characteristics of variable degrees of porosity, differential bioresorbability, compression resistance and radiopacity, and also maximizes the content of active ingredient relative to carrier materials such as collagen. Even more desirable would be a bone graft material that possesses all of the advantages mentioned above, and includes antimicrobial properties as well as allowing for drug delivery that can be easily handled in clinical settings. Embodiments of the present disclosure address these and other needs.